Method of making electric heaters



June 23, 1964 J. D. WILKINS METHOD OF MAKING ELECTRIC HEATERS 2 Sheets-Sheet 1 Filed Sept. 4, 1959 INVENTOR.

JOHN D. WI LKINS III W June 23, 1964 J. D. WILKINS METHOD OF MAKING ELECTRIC HEATERS 2 Sheets-Sheet 2 Filed Sept. 4, 1959 FIG-6 INVENTOR. JOHN D. WILKINS g w ragg A TTO/PNEYS United States Patent 3,137,924 METHOD OF MAKING ELECTRIQ HEATERS John D. Wilkins, St. Louis, M0-, assignor to Olin Mathieson (Chemical Corporation, East Alton, Iil., a corporation of Virginia Filed Sept. 4, 1959, Ser. No. 838,274 Claims. (Cl. 29-4555) This invention is directed to electric heaters and more particularly to sheathed resistance heaters and to a method for making the same.

Heretofore the manufacture of sheathed electric resistance heaters comprised the usual steps of positioning an electrical resistance element coaxially within a straight deformable tube of generally rounded cross-section while still straight, the tube was then filled with a heat-conducting electrical-insulating material such as magnesium oxide. Thereafter, in the manufacture of electric range hot plates and the like, the tube was then bent into a flat spiral of any appropriate radius, and then compressed radially to obtain the desired cross-sectional configuration, usually in a flat-top shape. During deformation of the tube into a flat spiral by bending operations, the insulating filler material is subjected to stresses which aften fragments it and causes voids which detract from reliability and eificiency of the unit. Also, during the alteration of the cross-section of the sheet by bending and pressing operations to obtain a desired shape, stresses are transmitted to the electrical element sheathed therein and cause the element-to fracture, thus, opening the circuit and rendering the heating unit useless. For more tortuous and extensive heaters than range hot plates, these disadvantages are aggravated. Where a heating element was desired to be tortuously or convolutely distributed within a common structure, the aforesaid sheathed heating unit has heretofore been shaped into the desired configuration of the desired structure, and molten metal was poured into the mold so as to be cast about the shaped sheathedheater unit. Various inherent disadvantages are present in the last said process. A particular one involves the introduction of additional barrier to heat transfer in the heat element in the form of the inner base formed between the metal of the structure and the metal of the sheet. Additional disadvantages that may be mentioned are those inherently present and referred to above resulting from deformation of the sheathed unit into desired spatial configuration about which the structure is molded.

Heretofore no process has been known or advanced for sheathing an electrical resistance element within a tubular structure extending in a tortuous curvilinear or multidirectional pattern.

Accordingly, it is an object of this invention to eliminate disadvantages of the prior art relating to the manufacture of such heaters.

Another object of this invention is to provide novel electrical heaters and a novel process for the manufacture thereof.

Another object of this invention is to provide a novel method for sheathing an electric resistance element within a tortuously extending tubular cavity.

A further object of this invention is to provide a novel method for sheathing an electrical resistance heating unit without subsequently disturbing insulating and conducting materials therein.

A still further object of this invention is to provide a novel solid electric heater having internally therein a tortuously extending cavity with an electrical resistance element sheathed therein.

FIGURE 1 is a plan View partly in section illustratingone embodiment of this invention for sheathing an elec- $337,924 Patented June 23, 1964:

ice

trical resistance element Within tortuous passages contained in a solid sheet structure;

FIGURE 2 is a perspective view illustrating a portion of novel means employed for sheathing an electrical resistance element according to the embodiment of FIG- URE 1;

FIGURE 3 is a sectional view taken along lines IIIIII of the embodiment of FIGURE 1;

FIGURE 4 is a partially sectional view illustrating one suitable type of an electrical resistance element to be sheathed in the embodiment of FIGURE 1;

FIGURE 5 is a sectional view of another electrical resistance element that can be sheathed in the embodiment of FIGURE 1;

FIGURE 6 is a plan view partially in section illustrating another embodiment of this invention;

FIGURE 7 is a sectional view taken along lines VII- VII of the embodiment of FIGURE 6;

FIGURE 8 is a perspective view of a portion of another novel means for sheathing an electrical resistance element in the embodiment of FIGURE 6;

FIGURE 9 is a cross-sectional view taken along lines IXIX of FIGURE 8; and

FIGURE 10 is a sectional view illustrating an electrical resistance element sheathed in the embodiment of FIG- URE 6.

In accordance with this invention the above objects and other objects can be obtained by fluid driving the electric conductor and insulation together as a unit into a platelike sheath. This is done, for example by attaching an electrical resistance element to a travelling leader plug which is propelled through tortuously a preformed pattern of extending inchoate hollows of uniform width which are contained within a solid structure and which at some stage fit the plug. Generally speaking, this is accomplished by mounting a plurality of insulating members at suitably spaced points on the resistance element, one end of which is attached to the aforesaid leader plug. The leader plug is then inserted into one end of the tortuously extending hollow to be filled and propelled therethrough by some appropriate means. In one embodiment fluid injection and inflation are contemplated. The hollow containing the heater structure may be of any desired final configuration, such as cubic, spheroidal and the like. The invention, however, will be described with reference to the patterned panels obtained by the well known roll forged process disclosed in the patent to Grenell, US. No. 2,690,002 granted on September 28, 1954.

In the process of the aforesaid patent, a pattern of weld-inhibiting material is interposed between superposed component sheets of metal and the sheets secured together to prevent relative movement therebetween. The secured superposed sheets are then welded together, as by hotrolling, in the adjacent areas thereof which are not separated by the weld-inhibiting material. The particular pattern of weld-inhibiting material may be applied in any desired configuration to define any desired complex system of passageways depending on the particular application desired for the welded unit. Upon welding of the unseparated portions of the welded unit, the applied pattern of weld-inhibiting material results in an unjoined portion or laminations extending between the sheets and between the unjoined portions thereof. These unjoined portions are then permanently distended by expansion thereof with fluid pressure and the like to form the desired system of tubular passageways. The welded sheets may be utilized in various ways, such as baseboard heaters or refrigerator evaporator plates and the like. Also, these welded sheets may be, either prior to or subsequent to expansion of the laminations therein, further fabricated into any structural configuration desired, as for example bending of the refrigerator evaporator plate to define a freezer compartment within a refrigerator. For the purpose of this invention, the panel before injection of the heater may be fully inflated, only partially inflated, or not inflated at all. Both of the latter are preferred, especially the last which enables simultaneous inflation and injection.

More specifically, with reference to FIGURE 1, a pressure-welded panel, such as obtained by the process of the aforesaid patent, is generally indicated as 1. This panel was formed from two component sheets 2 and 3 between which was interposed a pattern of weld-inhibiting material 4 in a pattern defining a convolutely wound system of unjoined portions or laminations. The electrical resistance element 5, such as the nickel-chrome alloy types, to be sheathed within panel 1 has mounted thereon a plurality of spacer members 6. Generally, these elements are flexible and of sufiicient strength to resist breakage when subjected to the tensile forces required for sheathing it Within panel 1. The element may comprise a wire 7 or a wire coiled into helical form 8, or if desired, may be helically coiled about an electrically insulating thread, such as glass, for support thereon.

The spacing members 6 are bead-like members of a material such as magnesium oxide that is heat-conducting but electric-insulating, they may be of any suitable configuration desired, but preferably the spacers are spheroidal, such as round beads, or discus-shaped, all strung on the conductor. These spacer members are mounted at spaced points on the resistance element in a suitable or convenient manner. However, it is not necessary that the members themselves may abut each other as illustrated in FIGURE 5. However, if the members are spaced from each other, it is only necessary that they be such as to prevent sagging of the resistance element, in its extended form within the sheet.

The members may be mounted on the resistance element by embedding the element during the molding of the members as indicated at 9 in FIGURE 4 or the resistance element may be threaded through suitable apertures in the members as in 10 at FIGURE 5. These members functionas supporting means for the resistance element within the sheet and also to space the resistance element from the inner wall of the sheet to prevent shorting therewith.

The size of the spacing members as will be understood is dependent on the cross-section of the sheet, and the spacing member may have a maximum cross-sectional dimension equal to corresponding dimensions of the mternal cross-section of the subsequently distended tubular hollows in the sheet. However, the spacing member is preferably smaller than the internal cross-section of the distended lamination for purpose hereafter discussed. The electrical resistance wire for convenience may be mounted on a spool 11 mounted within a suitable container 12 having a pressurizing conduit 13 and an outlet port 14 from which extends any suitable nozzle 15, flexible or rigid, the end of which is inserted into the unjoined portion 4 at 16. In order to insert nozzle 15 into the laminations, the laminations may be pried apartand distended at 16 to provide a suitable opening for reception of the nozzle end.

One end of the resistance element 5 is suitably attached to stem 10 by threading the end of the element through an opening 17 and securing it therein by looping the thread upon itself as at 18. Stem 10 is integral with the flared end 19 of a pilot or leader plug 26. This plug flares outwardly and rearwardly from a common point 21 to a terminal portion 22 having the cross-section necessary to provide the necessary distention of lamination 4 when the plug is propelled therethrough. As in the instant embodiment, the cross-section of the terminal portion 22 of plug will generally correspond to the crosssectional configuration 23 desired in distended unjoined portion 4.

In the sheathing operation of this invention, plug 20 may be positioned at any portion within nozzle 15, the

- a source of electrical current.

terminal end of which is inserted into the unjoined portion 4 at the opening provided at 16. After insertion of nozzle 15 into the unjoined portion 4, appropriate fluid pressure is then injected into container 12 at a sufiicient level to propel or drive the leader plug 20 through the unjoined portion 4 until the plug emerges from the sheet at the unjoined portions terminal end 24. Upon travel of the leader plug through the unjoined portion 4, each portion thereat is distended to assume the cross-section indicated by 23. Since metal inherently has spring-back so that it will recover after removal of stresses applied against it, the terminal portion 22 of leader plug 20 has preferably larger cross-sectional dimensions than corresponding dimensions of spacer members 6. The difference between corresponding cross-sectional dimensions of the spacer member and the terminal portion of the plug is generally equal to the amount of recovery in the metal at maximum corresponding portions of leader plug 26. If desired, although not required the distended unjoined portions 4 may be additionally shaped by positioning the panel between spaced apart platens at a suflicient distance to constrain the flat top portion 27 of tubular cross-section 23 against the flat top portion 28 of the terminal portion 22 provided in leader plug 20.

As will be understood, any fluid, as air, water, steam, and the like, may be employed provided it can be con veniently removed or driven off, as for example byevaporation, without leaving any electrically conducting residue to short out the resistance element. Preferably the propelling fluid is a slurry of material such as magnesium oxide which is heat-conducting and electrically insulating. This slurry may be contained within container 12 and the pressurizing fluid injected into conduit 13 on the slurry 25. In order to obtain the objectives of this invention, it is only necessary that the consistency of the slurry have sufficient viscosity to propel leader plug 20 through the unjoined portion 4 within panel 1. After the resistance element 5 with the spacing member 6 mounted thereon is sheathed within the distended unjoined portion 4, the slurry may be contained within the distention, and the liquid portion suitably driven off as by'the application of heat thereto.

As will be noted, this embodiment in addition to sheathing an electric resistance element within panel 1, simultaneously distends'the unjoined portion within which the resistance element is contained. As will be noted with reference to FIGURE 3, the resistance element may be directly sheathed into tortuously extending tubular passages contained within a solid structure. Such sheathing 0f the resistance element requires no additional barrier of metal between it and the inner walls of the structure.

FIGURE 6 illustrated another embodiment of this invention employing a different panel 29 fabricated in accordance with the process of the aforesaid patent to Grenell. However, the instant panel differs over the panel of the preceding embodiment in that the stop-weld material interposed between component sheets is provided in two distinct patterns 30 and 31 extending sinuously along the length of the panel with the pattern 30 returning by means of a straight portion 32 back to a position adjacent its point of entry. The pattern 30 is intended for subsequent sheathing of electrical resistance element 5' with spacing members 6 mounted thereon.

Pattern 30 is returned adjacent its point of entry in order to facilitate subsequent attachment of the ends of resistance elements to a suitable plug for attachment to The instant embodiment differs over the previous embodiment in that the resultant unjoined portion Within panel 29 defined by the patterns of weld-inhibiting material are distended prior to insertion of the resistance element 5. Also as illustrated, the unjoined portions 30 and 31 are distended so that the resultant tubular passages 33 and 34, respectively, are bulged out on only one side of panel 29. Such a one sided distention may be accomplished by conventional methods, for example as illustrated in US. Patent No. 2,866,429.

As with the preceding embodiment, nozzle 35 of a fluid reservoir 36 is inserted at 37 into the inlet of tubular passage 33. Appropriately coiled resistance element 5 having spacing member 6 mounted thereon, and having an end of the element attached to a leader plug 38 is suitably inserted within reservoir 36, as for example as by being wound on a spool suitably mounted within the reservoir. The reservoir is preferably filled with a slurry of material, such as magnesium oxide which is heat conducting and electrically insulating, and the slurry appropriately pressurized to propel or drive the leader 38 through the tubular passages 33.

Upon being propelled through passages 33, the leader plug 38 with the resistance element secured therethrough sheaths the resistance element within the passage after which the slurry is retained therein and the liquid portion of the slurry driven off.

For this embodiment, the leader plug is illustrated as a hollow cupped structure flaring outwardly from a common point 39 to its open end 40, the terminal portion 41 having a configuration corresponding to the distended passage 33. Suitably secured to the forward interior portion of leader plug 38 by suitable means 42, such as solder or weld, is a stem 43 of any suitable material, such as a strong Wire band of metal and the like extending externally out of leader plug 38 with the external end thereof formed into a loop 44 to which an end of the resistance element is appropriately secured.

Where no further distention of tubular passage 33 is desired, leader plug may have its cross-sectional dimension identical with the corresponding portions of tubular passages 33. Where such further distention is not desired, the leader plug 38 is fabricated of yieldable material having a thickness making the open end portions of the leader plug yieldable to the hydraulic pressures employed so that these open end portions will be radially flexible to snugly contact the inner walls of the leader plug and form an obturating seal against the hydraulic pressures employed.

As indicated above, the leader plug may be employed for further distending the tubular passages 33 upon being propelled therethrough. In such an operation, the portions of the leader plug adjacent the open end 40 may have a cross-sectional corresponding tube but somewhat larger than the internal cross-section of the tubes. With such a leader plug, the'terr'ninal portions 41 thereof further distend the tubular passages 33 upon passage to them to not only sheath the resistance element therein but in addition to size the passages to the desired cross-sectional configuration.

The element sheathed in the distended panel 29 advantageously provides an integral means for defrosting purposes when the panel is employed as an evaporator in refrigerators with the terminal portions of distended passages 34 attached into a circulating refrigerant system. Although the distended passages 33 and 34 have been illustrated as parallely coextending with each other, and in the same stratum within the panel, it is to be understood that the separate distended passages may also be provided in different stratums with each distended passageway system distended out of opposite faces.

Also, although the invention has been described with reference to specific embodiments, materials and details, various modifications and changes, within the scope of this invention, will be apparent to one skilled in the art and are contemplated to be embraced within the invention.

What is claimed is:

1. A method of sheathing an electric heating element in a solid and substantially rigid structure containing a continuous and unbranched hollow of substantially uniform cross-section extending in a multi-directional pattern therein, said method comprising mounting a plurality of heatconducting electric-insulating spacing members at spaced points on said element, attaching one end of said element to a traveling leader plug adapted to conform to the cross-section of said hollow in substantially sealing relationship therewith, inserting said plug in said hollow, hydraulically propelling said plug through remaining portions of said hollow under the direct influence of a fluid under sufiicient pressure to thread said element and mounted members in said hollow with said fluid comprising a slurry of a heat-conducting electric-insulating material and, including the step of retaining the solid portion of said slurry in said hollow.

2. A method of sheathing an electric heating element in a continuous tubular passage extending in a continuous, unbranced and multi-directional pattern within joined superimposed substantially rigid and ductile sheets and between joined portions thereof said method comprising mounting a plurality of heat-conducting electric-insulating spacing members at spaced points on said element, attaching one end of said element to a traveling leader plug adapted to conform in sealing relationship with said passage, inserting said plug in one end of said passage, hydraulically propelling said plug through remaining portions of said passage under the direct influence of a liquid filler medium comprised of a slurry of a heat-conducting electric-insulating material, and substantially eliminating the liquid portion of said slurry to provide in said passage a solid product from said slurry.

3. A method of sheathing an electric heating element in a tubular passage formed by distention of a continuous unwelded area extending in a continuous, unbranched and multi-directional pattern between welded superimposed ductile metal sheets and between welded portions thereof said method comprising mounting a plurality of heat-conducting electrio-insulating spacing members at spaced points on said element, attaching one end of said element to a traveling leader plug adapted to conform in sealing relationship with said passage, inserting said plug in one end of said passage, hydraulically propelling said plug through said passage under the direct influence of a liquid filler medium comprised of a slurry of a heat-conducting electric-insulating material, and substantially eliminating the liquid portion of said slurry to provide in said passage a solid product from said slurry.

4. A method of sheathing an electric heating element within unwelded and undistended portions contained between welded superimposed metal sheets and between welded portions thereof said method comprising mounting a plurality of heat-conducting electric-insulating spacer members at spaced points on said element, attaching one end of said element to the terminal end of a traveling leader plug flaring outwardly from a common forward point to a terminal portion having a cross-section required for imparting a desired internal cross-section in said unwelded portions upon subsequent distention thereof, forming an opening into one terminal end of said unwelded portion, inserting said plug in said opening, and hydraulically propelling said plug through said unwelded portion under the direct influence of a fluid with suflicient pressure for distention of said unwelded portion and threading of said element therein.

5. The method of claim 4 wherein said fluid is a slurry of a heat-conducting electric-insulating material with said plug hydraulically propelled with said slurry, retaining said slurry within the distended unwelded portion, and including the step of substantially eliminating the liquid portion of said slurry to provide in the distended unwelded portion a solid product of said slurry.

6. The method of manufacturing an electrically heated substantially rigid plate structure comprising forging a tube-in-sheet panel by selectively pressure welding together adjacent surfaces of superimposed sheets to define between said sheets interior areas of separation corresponding to at least one continuous passageway desired in said structure, distending said areas into said passageway inserting a traveling leader plug in said areas of separation with said plug being adapted to conform in sealing relationship with said passageway, attaching an electrical heating element to said plug, mounting a plurality of heat-conducting electric-insulating spacing members at spaced points on said element, inserting said element into a selected portion of said areas by propelling said plug through said areas of separation by applying directly against said plug a filler liquid medium pressurized in fluid flow relationship in said selected portion with said liquid medium being comprised of a slurry of heat-conducting material, and the step of substantially eliminating the liquid portion of said slurry to provide in said passage- Way a solid product in electrically-insulated relationship with said element.

7. The method of manufacturing an electrically heated substantially rigid plate structure comprising forging a tube-in-sheet panel by selectively pressure welding together adjacent surfaces of. superimposed sheets to define between said sheets interior areas ofseparation corresponding to a desired system of passageways containing a continuous bent passageway desired for insertion of an electrical heating element, distending said areas of separation into said system of passageways, inserting a travel ing leader plug into said passageway with said plug being adapted to conform in sealing relationship with said passageway, attaching said electrical heating element to said plug, mounting a plurality of heat-conducting electricinsulating spacing members at spaced points on said ele ment, inserting said element into said passageway by propelling said plug through said passageway by applying directly against said plug a liquid filler medium pressurized in fluid flow relationship in said passageway with said liquid medium beingcomprised of a slurry of a heat conductive electrically-insulating material, and the step of substantially eliminating the liquid portion of said slurry to provide in said passageway a solid product from said slurry.

8. A method for sheathing an electrical heating element in a hollow panel structure obtained by interposing between superimposed metal sheets a pattern of stop-weld material corresponding to a desired system of passageways with said sheets pressure welded together about said pattern to provide a system of internal unjoined areas defining said desired system of passageways wherein said desired system of passageways comprises a first system of 1 fluid passageways and a separate unconnected second sys tem defining a continuous tubular passageway, comprising distending said areas into said desired system of passageways and inserting into the portion of said unjoined areas corresponding to said tubular passageway a traveling leader plug having attached thereto said heating element with said plug being adapted to conform in sealing relationship with said passageway, said element having mounted thereon a plurality of heat-conducting electricinsulating spacing members at spaced points, hydraulically propelling said plug through remaining portions of said passageway under the direct influence of a pressurized liquid to thread said element in said passageways wherein said liquid comprises a slurry of heat conducting material, and the step of substantially eliminating the liquid portion of said slurry to provide in said passageway a solid product of said material in electrically-insulated relationship to said element.

9. A method for making a sheet metal heater comprising imposing between superimposed metal sheets an aggregate pattern of stop-weld material corresponding to a plurality of desired systems of passageways wherein said pattern comprises a first pattern corresponding to a first system containing a continuous tubular passageway and a second pattern corresponding to a separate unconnected second system of fluid passageways adapted to be distended with fluid pressure, forming a panel by pressure welding said sheets together about said aggregate pattern forming an opening into one terminal end of the unwelded portions of said panel defined by said first pattern, mounting at spaced points on an electric heating element a plurality of heat conducting spacer members in electricallyinsulating relationshipwith said element, inserting into said opening a substantially rigid traveling leader plug having a configuration corresponding to the desired crosssection of said passageway upon subsequent distention thereof with said plug having one end of said element attached thereto, and hydraulically propelling said plug through said unwelded portions under the direct influence of a fluid under sufficient pressure to permanently distend said unwelded portions upon travel therethrough and to thread said element therein.

10. The method of claim 9 wherein said fluid is a liquid medium comprised of a slurry of heat conductive electrically-insulating material, and including the step of substantially eliminating the liquid portion of said slurry to provide in said passageway a solid product of said material in electrically-insulated relationship to said element.

References Cited in the file of this patent UNITED STATES PATENTS 320,229 Delany June 16, 1885 554,910 Delany Feb. 18, 1896 557,258 Delany Mar. 31, 1896 942,184 Persons Dec. 7, 1909 979,899 Steigleder Dec. 27, 1910 1,247,125 Madsen Nov. 20, 1917 1,980,719 Egger Nov. 13, 1934 2,018,293 Williams et al Oct. 22, 1935 2,075,686 Wiegand Mar. 30, 1937. 2,470,338 Chilton Mar. 17, 1949 2,589,503 McCullough Mar. 18, 1952 2,729,424 Eppensteiner Jan. 3, 1956 2,777,300 Palmer Jan. 15, 1957 2,823,153 Bunnel et al. Feb. 11, 1958 2,853,764 De Michele Sept. 30, 1958 2,869,226 Schurman Jan. 20, 1959 2,920,377 Janos Jan. 12, 1960 3,010,091 Sawyer Nov. 21, 1961 3,031,735 Jepson May 1, 1962 

1. A METHOD OF SHEATHING AN ELECTRIC HEATING ELEMENT IN A SOLID AND SUBSTANTIALLY RIGID STRUCTURE CONTAINING A CONTINUOUS AND UNBRANCHED HOLLOW OF SUBSTANTIALLY UNIFORM CROSS-SECTION EXTENDING IN A MULTI-DIRECTIONAL PATTERN THEREIN, SAID METHOD COMPRISING MOUNTING A PLURALITY OF HEATCONDUCTING ELECTRIC-INSULATING SPACING MEMBERS AT SPACED POINTS ON SAID ELEMENT, ATTACHING ONE END OF SAID ELEMENT TO A TRAVELING LEADER PLUG ADAPTED TO CONFORM TO THE CROSS-SECTION OF SAID HOLLOW IN SUBSTANTIALLY SEALING RELATIONSHIP THEREWITH, INSERTING SAID PLUG IN SAID HOLLOW, HYDRAULICALLY PROPELLING SAID PLUG THROUGH REMAINING PORTIONS OF SAID HOLLOW UNDER THE DIRECT INFLUENCE OF A FLUID UNDER SUFFICIENT PRESSURE TO THREAD SAID ELEMENT AND MOUNTED MEMBERS IN SAID HOLLOW WITH SAID FLUID COMPRISING A SLURRY OF A HEAT-CONDUCTING ELECTRIC-INSULATING MATERIAL AND, INCLUDING THE STEP OF RETAINING THE SOLID PORTION OF SAID SLURRY IN SAID HOLLOW. 